The invention relates generally to powder magnetic material and is related more particularly to a means for stabilizing the magnetic properties of sintered rare earth-cobalt magnets.
Generally, in powder material fabrication of magnets, such as rare earth-cobalt magnets, for example, the elemental components are mixed in a molten state to produce a desired composition material. The composition material usually is ground to a fine powder which then may be compacted into a desired configuration while exposed to a particle aligning magnetic field. After degaussing, the compacted device may be subjected to suitable sintering temperature for producing shrinkage and greater densification of the compacted powder material. As a result, the aligned powder particles are bonded to one another; and the magnetic properties of the composition material ae greatly enhanced. Accordingly, when the sintered material is magnetized in the direction of particle alignment, a device having high magnetic coercivity and energy product is produced.
After sintering, it may be found that the packing density of the compacted material has increased to as much as 97 percent of a theoretical maximum value, which is determined by dividing the weight per unit volume by the density of the material. It is well-known that greater densification of the powder material would produce a correspondingly higher magnetization and energy product levels. However, if the sintering temperature is increased to achieve a greater packing density of the powder material, excessive grain growth may occur and cause a significant loss in magnetic coercivity. Consequently, it is common practice to select a compromise sintering temperature which will provide adequate densification of the powder material while avoiding excessive grain growth during the sintering operation.
Therefore, it is advantageous and desirable to provide a magnetic powder material having means for increasing packing density and curbing grain growth during the sintering operation.